Minimal version of Qt 5.2 is false in Requirements

[gilga]

I’ve tried to build Speedcrunch on my Qt 5.4 and it didn’t work:

QtFontmetrics class was missing some function named “horizontalAdvance”.

Actually this function was introduced only in Qt 5.11.

https://doc.qt.io/qt-5/qfontmetrics.html#horizontalAdvance

I think it’s safer to put the minimal version as “Qt 5.15.0”.

[Helder Correia]

Up the minimum Qt version to 5.15

Fix issue #1150.

→ <<cset 2cd580bf05bf>>

[Helder Correia]

Fixed in commit https://bitbucket.org/heldercorreia/speedcrunch/commits/2cd580bf05bfe2775fa8e97d7bb4b2e68a52ec60